1. Field of the Invention
The present invention relates to hard disk drives; more particularly, to hard disk drives which have reduced size and weight, and increased storage capacity.
2. Description of the Related Art
Data storage technology follows a continuing trend towards increasing storage density, and reducing device weight, size, and power consumption. One factor motivating these trends is the increasing use of lap-top, notebook, palm-top, and other portable and/or battery-powered computers. Portability requires reduced size (physical dimensions) and weight. Increased storage density is necessary so that a disk drive having a reduced physical size can provide the same storage capacity as a physically larger drive.
The dimensions of disk drives have generally become standardized around certain so-called "form factors." Eight inch (8") disk drives were followed by the five and one-quarter inch (51/4") disk drives. The length of a 51/4" drive is approximately the width of an 8" drive and the width of a 51/4" drive is approximately one-half of the length of an 8" drive. This same size relationship applies to the relationship between so-called three and one-half inch (31/2") drives and 51/4" drives (a 31/2" drive is approximately one half the size of a 51/4" drive), and to the relationship between two and one-half inch (21/2") drives and 31/2" drives (a 21/2" drive is approximately one half the size of a 31/2" drive).
In addition, the heights of disk drives have changed. Initially, this relationship followed a trend similar to form factors, full height 51/4" drives were reduced to half-height 51/4" drives (a height of approximately 1.625"). The half-height form factor was the starting point for 31/2" drives, which were later reduced to a one inch (1.0") height form factor and lower. For 21/2" form factor disk drives, a typical height is in the range of 0.71"-0.75", generally depending on whether the drive has one or two disks. With the increasing popularity of portable and notebook computers, the thrust toward reduced size and increased capacity remains extremely strong.
Typically, Winchester-type hard disk drives incorporate a storage medium or disk, read-write transducers or "heads" to transfer information to and from the disks, a spin motor for rotating the disks, an actuator assembly for positioning the heads with respect to the disk, and control electronics (usually on a printed circuit board) incorporating means for communicating with a host computer, means for controlling data transfer functions to and from the disk, and means for controlling the integral components of the disk drive. A number of Winchester-type hard disk drive designs incorporate the disk, heads, actuator assembly and spin motor within a controlled environment, isolated from ambient atmospheric conditions. Generally, the controlled environment is provided in the hard disk assembly (HDA) portion of the drive which, along with the control electronics, may comprise an integrated mechanical assembly substantially (or totally) defining the desired form factor.
The HDA generally comprises: a base, on which the disk, heads, actuator assembly, spin motor, and connectors are mounted;, and a cover, which forms an intersecting fit with the base and encloses the components in the drive, thereby creating the controlled environment between the base and cover. A gasket may be provided between the cover and the base to ensure a seal therein between. Typically, such drives can withstand pressure changes in a range of 200 feet below sea level to 10,000 feet above sea level.
Because of the sensitivity of the components contained within the controlled environment, contamination is a major cause of drive failure. The prevention of contamination within the drive is thus a specific and important design goal. As the overall size of the disk drives has decreased, so has the volume within the controlled environment surrounding the contaminant sensitive elements of the drive. In two and one-half inch form factor drives, the reduced size of the controlled environment has resulted in contamination problems resulting from outgassing, e.g. the tendency of certain materials used in manufacturing the drive to exude gasses within the controlled environment over the life of the drive. Outgassing causes a buildup within, and eventual release of pressure from, the controlled environment. Such a release allows contamination to enter the drive, which may thereby compromise data integrity.
Materials known to cause outgassing problems are pressure sensitive adhesives. Adhesives, such as Part No. Y-9460 pressure sensitive adhesive, manufactured by Minnesota Mining and Manufacturing (3M) Company, St. Paul, Minn., are typically used at various stages in drive manufacture. Such pressure sensitive adhesives are used in a number of sub-assemblies in the controlled environment. For example, in an actuator assembly, which typically consists of an actuator body, having read/write heads coupled thereto, and a bearing cartridge, which allows the actuator body to rotate (generally about a post) on the base plate, adhesives are used to secure the bearing cartridge to the actuator body. In another aspect, adhesives are used to secure the spin motor to the base plate. Further, many drives incorporate flex circuits to carry data from the printed circuit board to the actuator. The flex circuit has one end coupled to the actuator and another end coupled to a bracket and header, which couples the circuit to the PCB. In such applications, adhesives are used in securing both ends of the flex circuit.